The Earth's atmosphere consists mainly of nitrogen and oxygen. It also contains smaller amounts of other gases and particles, including ozone that protects us from harmful ultraviolet rays and greenhouse gases that trap some of the sun's rays to maintain the earth's surface temperature at levels able to support life.

However, some human activities change the nature of the atmosphere, affecting air quality, levels of ultraviolet (UV) radiation and the amount of greenhouse gases (such as carbon dioxide and methane). For example, the burning of fossil fuels (e.g. coal, oil and gas) has greatly added to the atmospheric levels of the greenhouse gas carbon dioxide, while the clearing of forests and grasslands has reduced the capacity to remove carbon dioxide from the atmosphere.

Emissions of substances into the atmosphere are considered in this section under three main categories: greenhouse gas emissions, air pollutants and ozone depleting substances.

Greenhouse gas emissions

The main naturally occurring greenhouse gases (GHGs) in the earth's atmosphere are carbon dioxide and water vapour. The increased heating effect arising from increasing levels of GHGs in the atmosphere is known as the greenhouse effect and has been linked to global warming and climate change. A 2007-08 ABS survey of households indicated that nearly three-quarters (73.5%) of Australians were concerned about climate change.

The main GHGs generated by human activities are carbon dioxide, methane and nitrous oxide. Smaller amounts of hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride are also emitted. Carbon dioxide is by far the dominant GHG, accounting for about 74% when expressed as carbon dioxide equivalents (CO2-e). CO2-e is a measure used to take account of the different types of GHG emissions on a common basis.

Australia's total GHG emissions in 2007 were 9% greater than in 1990 (graph 3.24). Carbon dioxide emissions were 10% greater, methane emissions were 0.4% less, and nitrous oxide emissions were 24% greater. When Australia ratified the Kyoto Protocol its goal was to limit net GHG emissions to 8% above the 1990 levels across the period 2008-2012.

Australia reduced its greenhouse gas emissions per capita by 11.3% over the period 1990 to 2007 (from 31.8 tonnes CO2-e/capita in 1990 to 28.2 tonnes CO2-e/capita in 2007).

When Australia's GHG emissions are related to economic activity, as measured by Gross Domestic Product (GDP), it can be seen that there has been a steady decline in the amount of GHG emissions relative to GDP over the period 1990 to 2007. In 1990, the rate of emissions was 897.5 tonnes of CO2-e per $million of GDP, decreasing to 559.6 in 2007, a fall of 38%.

Although the Australian economy (GDP) grew by 75% between 1990 and 2007, the nation's net GHG emissions grew by only 9%. The falling trend in emissions per unit of GDP has been attributed to better management of emissions across sectors, the large decline in land use change emissions, and stronger growth in the services sector rather than in the more energy intensive manufacturing sector.

Main sources of greenhouse gas emissions

Carbon dioxide

Most of Australia's carbon dioxide emissions occur as the result of fuel combustion. In 2007, fuel combustion accounted for 81.5% of the nation's total carbon dioxide emissions.

The energy industries, in particular electricity generation from coal-fired stations, accounted for 60% of fuel combustion emissions in 2007, up from 56% in 1990. Road transport accounted for 18% of fuel combustion emissions in 2007.

3.25 carbon dioxide emissions (a): energy and transport

Between 1990 and 2007, carbon dioxide emissions from fuel combustion increased by 44.5%. Within the fuel combustion activities, energy industries showed an increase of 55% and road transport was up 25% in this period (graph 3.25).

Of note is the comparison between passenger vehicle fuel consumption and carbon dioxide emissions for the period 1998 to 2007. The former increased by 21% between 1998 and 2007, whereas the latter increased by 7%. From 2005, carbon dioxide emissions by passenger vehicles are seen to have decreased compared to fuel consumption (graph 3.26), which may reflect a move towards the use of liquefied petroleum gas (LPG) which has a lower carbon dioxide emission factor than other fuels.

3.26 PASSENGER VEHICLES - CO2 emissions & fuel consumption

Methane

When expressed in CO2-e, methane comprised 19.7% of Australia's total GHG emissions in 2007, compared to 21.6% in 1990.

The digestive processes of livestock (enteric fermentation) and fugitive emissions from coal mining together account for more than two-thirds of Australia's methane emissions (graph 3.27).

When expressed in CO2-e, nitrous oxide comprised 4.1% of Australia's total GHG emissions in 2007, compared to 3.6% in 1990. Nitrous oxide emissions are mainly the result of the use of nitrogen-based fertilisers and manure.

Very small contributions to GHG emissions are made by the hydrofluorocarbons (HFCs), the perfluorocarbons (PFCs) and sulphur hexafluoride that are used in refrigeration and air-conditioning equipment, fire extinguishers, aerosol cans and electrical equipment. The combined contribution of these gases to the total GHG emissions has been around 1% or less over the period 1990 to 2007.

Air pollutants

The state of our air is an important factor in the quality of life. Air pollutant levels are not considered to be high in urban Australia (relative to other world cities). However, poor air quality can have a range of negative effects, from causing health problems and reducing crop yields to harming flora and fauna.

The main air pollutants in outdoor (or ambient) air are carbon monoxide, nitrogen dioxide, photochemical oxidants (as ozone), sulphur dioxide and particles (dusts). The National Environment Protection Measure for Ambient Air Quality (the Air NEPM) sets standards for the maximum concentrations of key air pollutants which all Australian jurisdictions are legally bound to meet.

Carbon monoxide is generated during the burning of carbon containing substances, either in the form of fossil fuels or as vegetation. In 2007, the prescribed burning of savannas (grasslands) by the agriculture sector generated over four times as much carbon monoxide as the energy sector (table 3.28).

The main source of sulphur dioxide emissions is industrial activity including copper, lead, zinc, nickel and silver processing.

Nitrogen dioxide is an important air pollutant because it contributes to the formation of photochemical smog, which is another health hazard. The burning of fossil fuels, (coal, oil and gas), is a major source of nitrogen dioxide. Most of the nitrogen dioxide in cities comes from motor vehicle exhausts (about 80%).

Particulate matter (mainly smoke and dust) emissions are reported in the National Pollution Inventory (NPI). Two sizes of particle are measured, 10 micrometres or less in diameter (PM10) and 2.5 micrometres or less in diameter (PM2.5). These particles are of a size that can be inhaled and hence pose a health hazard to humans (and animals). Besides being a health hazard, particulate matter can affect the aesthetics and utility of areas through visibility reduction, and may affect buildings and other structures and vegetation.

PM2.5 is mainly emitted by coal-burning electricity generating plants and by mining operations. Bushfires and dust storms add to the burden of smoke and dust exposure. Within a given region, or population centre, the exposure to these particles will vary according to the local activities e.g. in Adelaide the suburb of Netley, next to Adelaide Airport, exceeded the levels for PM10 on 11 days in 2008, while the residential suburb of Kensington Gardens registered one day of exceedence in that period.

It should be noted that the measurements relate to the amounts generated at the source and therefore exposure to humans and the environment to pollution cannot be determined by the NPI. Industrial/mining emissions are estimated from reports provided by industry, while others, such as windblown dust, bushfires, and motor vehicles are estimated by state authorities (table 3.29).

Ozone depleting substances

The ozone layer is a naturally occurring layer of the upper atmosphere where harmful ultraviolet radiation from the sun is filtered out. Ozone depleting substances (ODSs) can break down the ozone layer, allowing more harmful radiation to penetrate.

3.29 Particulate emissions 2007-08

PM10

PM2.5

Source

kilograms/yr

kilograms/yr

Metal ore mining

270 000

9 100

Burning (fuel reduction, regeneration, agricultural) / Wildfires

240 000

-

Coal mining

210 000

4 600

Windblown dust

190 000

-

Paved/unpaved roads

160 000

-

Electricity generation

27 000

10 000

Solid fuel burning (domestic)

20 000

-

Motor vehicles

12 000

-

Basic non-ferrous metal manufacturing

11 000

920

Water transport

11 000

790

Oil and gas extraction

2 400

3 100

Log sawmilling and timber dressing

1 300

770

- nil or rounded to zero (including null cells)

Source: Department of the Environment, Water, Heritage and the Arts, National Pollution Inventory.

Data collected in the upper atmosphere have shown a general thinning of the earth's ozone layer, including a 5-9% depletion over Australia since the 1960's. The Antarctic ozone hole is a thinning of ozone in the stratosphere over Antarctica each spring.

The main classes of ODSs are chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons and methyl bromide. Australia was a signatory to the Montreal Protocol in 1989, whereby countries agreed to phase out the use of ODSs. The use of CFCs, traditionally used in refrigeration and aerosols, has largely been replaced by hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs), which are synthetic greenhouse gases. Emissions from HFCs and PFCs increased almost five-fold between 1990 and 2007, but in total they contribute 1% or less to Australia's total greenhouse gas emissions.